Jet turbine lubricant composition



United States Patent JET TURBINE LUBRICANT COMPOSITION William T.Stewart, El Cerrito, and George J. Benoit, In, San Anselmo, Calif.,assignors to California Research Corporation, San Francisco, Calif, acorporation of Delaware No Drawing. Application May 10, 1956 Serial No.583,921

3 Claims. (Cl. 252-325) This invention relates to a novel lubricantcomposition, and it is particularly directed to the provision of alubricant which is especially suitable for use in jet engines employedin aircraft.

Lubricating oils used in jet engines are subjected to operatingconditions so severe that few if any oils are available which aresatisfactory in all particulars. The chief causative factor leading tooil failure in jet aircraft engines is the high temperature-550 to 650F. or even higher-of many of the surfaces with which the lubricating oilcomes in contact. Such temperatures normally induce rapid carbonformation, or coking in the oil and also greatly accelerate oxidativedeteroriation of the oil in the presence of air. Further, the geartrains employed in jet engines are highly loaded and impose severeextreme pressure and anti-wear conditions on the lubricant. Sinceaircraft must operate at abnormally lowtemperatures such as thoseencountered in the arctic and at high altitudes, it is also essentialthat the oil be adapted for use at both high as well as lowtemperatures.

In order for a lubricant to meet the severe operating conditionsencountered in jet aircraft service, it is neces sary that it possess anumber of outstanding characteristics. Thus, the volatility must be lowin reference to the viscosity in order to maintain a reasonably low oilconsumption rate at high operating temperatures; further, theviscosity-temperature characteristics of the oil must be such as topermit starting of the engine at temperatures well below 50 F., yet giveexcellent lubrication at the temperatures of 550 to 650 F. encounteredin operation. The pour point of the oil must be below 65 F. Since theoil used in gas turbines comes in contact with a variety of metals, itmust be noncorrosive to steel, aluminum, magnesium, copper and bronze,and preferably to silver as well. Because of the high gear loadingsemployed in jet engines, it is necessary that the oil be supplied withadditives which impart good end point and anti-wear qualities. Further,it is necessary that the oil be supplied with oxidation inhibitoradditives as well as with metal deactivating agents in order to combatthe deleterious eifect of the high temperatures encountered in theengine. There is a wide variance between oils in their response tooxidation inhibitor additives, and it is therefore important not only toemploy such additives, but to use as the base fluid an oil which gives agood inhibitor response. Lastly, from the standpoint of engineperformance, it is also important that the oil have substantially nofoaming tendencies, which quality can be imparted by the addition of ananti-foaming agent.

Aside from the foregoing engine-performance characteristics, it is alsoof great importance that a jet lubricant have certain other qualities aswell. Thus, it should be compatible with and not attack the variousrubber packings, rings and hoses, as well as the paint and electricalinsulating materials which come into con- "ice.

tact with the oil either continuously, or during periods of enginefailure or servicing.

It is known that the desired pour point, volatility andtemperature-viscosity characteristics required in a jet turbinelubricant can best be met by synthetic oil rather than a mineral oil.Such synthetic oils include oils obtained by polymerization of lowermolecular weight alkylene oxides such as propylene and/or ethyleneoxide. One of the better types of synthetic oil hitherto proposed foruse as the base fluid of a jet turbine lubricant is believed to be analkyl diether of poly-1,2-oxypropylene glycol, and a jet lubricantcomposition based on this glycol diether is described and claimed incopending application Serial No. 383,386, filed September 30, 1953, nowPatent No. 2,801,968. However, while this glycol diether base fluid haslittle inherent tendency to form coke at the elevated temperatureencountered in jet aircraft engines, this is not the case when this basefluid has been supplied with the conventional extreme pressure,oxidation inhibitor, anti-wear, metal deactivator and foam inhibitoradditives which are necessary.

As described in the aforesaid copending application, it is possible toreduce the coking tendencies of the compounded oil from values in therange of about 800 to 1000 (as determined in the coking test describedin the examples below) to those of approximatelyBOO to 350 by the use ofa particular combination of additives which prove noncorrosive to allthe metals encountered in jet engines. While the resulting lubricantcomposition is satisfactory for use in jet aircraft engines wherein thesurface temperatures encountered by the oil do not exceed about 525 to575 F. (or even 600 F. for short periods of time), such oils cannot beemployed in the latest types of jet aircraft engines where thetemperatures encountered by the oil are in the range of 600 to 650 F.and even higher. For such engines the present military requirement isthat the oil, in addition to being noncorrosive to steel, aluminum,magnesium, copper and silver, shall have a coking value which is notmaterially greater than about 100. Accordingly, it is an object of thepresent invention to provide a jet turbine lubricant composition whichwill meet this, as well as the other significant requirements of themilitary and civilian specifications for jet engines operated attemperatures above 600 F.

It is our discovery that the foregoing object is achieved in aparticular embodiment of the invention by employing a lubricantcomposition which, in addition to the defined additive components, asdescribed in succeeding portions of the specification, incorporates asthe base fluid an alkyl diether of a mixed oxyethylene-l,2-oxypropyleneglycol polymer. It was found that quite unexpectedly, and for no reasonof which applicants are aware, the said mixed polyglycol diethers notonly possess an intrinsically low coking value, but also have theability to be compounded with certain extreme pressure, oxidationinhibitor, anti-wear, metal deactivator and foam inhibitor additives toprovide finished lubricant compositions which have coking values belowand can be employed with outstanding success in jet engines operated attemperatures well above 600 F. without giving rise to coking, corrosion,or other difficulties,

oils as well as with the diester types of synthetic oils} 3 therebypermitting blending with said oils under emergency conditions withoutharm to the engine.

The present composition is made up in major pro portion, preferably fromabout 90 to 98%, of an alkyl diether of a polyalkylenc glycol which isessentially comprised of a mixture of oxyethylene and l,2-oxypropyleneunits. While the commercially available mixtures of ethylene oxide andpropylene oxide from which the present polyglycol materials are preparedmay contain minor amounts of other glycols such as 1,3-propylene oxideor the various butylene oxides, as a practical matter these materialscan be disregarded and the polyoxyalkylene glycol diether base fluid ofthe present composition can be expressed as being a material of the typehaving the general formula wherein the designated oxyethylene and1,2-oxypropylene groups are randomly distributed in the molecule, andWhere n has a value of at least one, In has a value of at least two, Rand R represent alkyl groups of from 1 to 18 carbon atoms each, andwhere the molecular weight (or average molecular Weight) is between 350and 700, of which at least 250 is attributable to the oxyethylene and1,2-oxypropylene groups apart from the R and R end groups.

As has been indicated above, it is also contemplated that the mixedpolyglycol molecule may contain a relatively small percentage (notgreater than about or of other oxyalkylene units such as oxytrimethyleneandthe various oxybutylene groups, for example, since the latter arecommonly found in many commercially available C and C oxide startingmaterials. However, inthe preferred compositions of this invention theoxyethylene and 1,2-oxypropylene units are substantially the onlyoxyalkylene units present in the molecule apart from the ether-linkedalkyl end groups.

In the preferred compositions of the present invention, the mixed C --Cpolyglycol diethers are those of the type wherein one of the alkylradicals designated by R and R contains from 1 to 3 carbon atoms, Whilethe other of said radicals contains from 4 to 10 carbon atoms. Further,the molecule preferably contains from 33 to 75 mole percent of1,2-oxypropylene groups, and, conversely,

from 67 to 25 mole percent of the oxyalkylene groups.

As regards physical properties, the preferred polyglycol diether basefluids have viscosities between about 5,000

and 12,000 cs. at 65 F. and between about 2.5 and 3.5 cs. at 210 F.,these figures all being determined in the absence of any additive, orcompounding ingredients. All of the diether base fluids of the typedescribed above have pour points below about 65 F. and flash pointsabout about 350 F.

In general, the C C polyglycol diether base fluids of the presentinvention, as prepared by conventional methods, will represent mixturesof varying chain length and molecular configuration. Accordingly, thedata given above and eleswhere herein is to be taken as eitherdescribing individual polyglycol diether compounds or mixtures of saidcompounds, in which latter case the data given refer to the averagevalues evidenced by the mixture as a whole.

The C -C polyglycol diether base fluids described above are generallyknown in the art and are of the type described, for example, in U. S.Patent No. 2,425,755, issued August 19, 1947, to Roberts et al. Thepresent polyglycol diethers are normally prepared by reacting a mixtureof ethylene and 1,2-propylene oxides (in the proportion of 33 to 75 molepercent'of the propylene oxide'to from 67 to 25 mole percent of thepropylene oxide) with a minor amount (usually from about 8 to 20 molepercent) of a monohydric aliphatic alcohol in the presence of analkaline catalyst. Following the completion of this reaction theresulting polymerization product is esterified so as to replace theterminal hydroxy group by an alkoxy radical, thereby forming thediether. The alcohol reacted with the 1,2-propylene oxide is a primaryor secondary monohydric alcohol such as methanol, ethanol, n-propanol,2-propanol, n-butanol, 2-methylpropanol, Z-butanol, n-pentanol,3-methylbutanol, Z-methylbutanol, n-hexanol, Z-ethylbutanol,2-methylpentanol, S-methylpentanol, n-heptan0l, Z-methylhexanol, 2,2dimethylpentanol, n-octanol, Z-ethylhexanol, isooctyl alcohol (a Calcohol prepared by way of the 0x0 synthesis), n-decanol, n-dodecanol,or the like. Generally speaking, any alcohol having a pour point belowabout F. can be reacted with the mixed ethylene-propylene oxides to produce a material which, When converted to the diether, will have a pourpoint below -65 F. If desired, mixtures of two or more alcohols can beemployed, thereby producing a mixture of polymeric material havingdifferent alkyl groups attached at the one end of the molecular chain.Preferably the alcohol employed to initiate the reaction is one ofbranched-chain configuration having from 4 to 10 carbon atoms.

The monoether products obtained by a practice of the method describedabove where the mixture of alkylene oxides is reacted with a monohydricaliphatic alcohol normally contain a free hydroxyl group at one end ofthe molecule and the ether-linked alkyl radical (which can be designatedas R in the structural formula given above) at the other end of themolecule. The polyglycol diethers of the present invention canthereafter be prepared by replacing the terminal hydroxyl group of themonoether intermediate with an alkoxy radical containing from about 1 to18 carbon atoms, though preferably from 1 to 3 carbon atoms, theresulting alkyl group which thus becomes linked to the molecule beingdesignated as R in the structural formula given above. Thisetherification can be effected by reacting the monoether, or mixture ofmonoethers, with a suitable alkyl sulfate in the presence of caustic,though the reaction is preferably effected by first reacting themonoether with a dispersion of metallic sodium to convert the polymer tothe corresponding sodium salt and then reacting the salt with thedesired alkyl chloride.

Instead of employing a monohydric alcohol of the type described above tosupply the R radical and initiate the polymerization reaction, themixture of ethylene and propylene oxide starting materials can bereacted with an u,,6-dihydric alcohol such as ethylene glycol or1,2-propylene glycol in the presence of a suitable catalyst. In thiscase the resulting polymer has a terminal hydroxy group at each end ofthe molecule and both of said groups are replaced by alkoxy groups in asubsequent etherification of the type described above. Still othermethods of preparation will suggest themselves to those skilled in theart.

The lubricant compositions of the present invention are suitablyprepared by combining polyglycol diether base fluids of the typedescribed above with the particular additive which has been found togive the desired final product, as will w be described.

As the oxidation inhibitor there is employed from 0.2 to 5%, andpreferably from 0.5 to 3%, by weight, of a compound selected from thegroup consisting of phenyl-ot-naphthylamine, phenothiazine and thedialkyl selenides such as dihexyl selenide, didodecyl selenide, hexyldodecyl selenide, di(2-ethylhexyl) selenide, dioctadecyl selenide,isooctyl hexadecyl selenide, and the like, wherein the alkyl groupsattached to the selenium atom contain from 6 to 18 carbon atoms each. Ofthese inhibitors, the preferred compound is phenyl-a-naphthylamine.

The extreme pressure additive is employed in the amount of from 0.05 to1%, and preferably of from 0.1

to 0.5% by weight. This compound is selected from the group consistingof alkylamine salts of acid alkyl esters of phosphoric acid and blendsof said salts with acid alkyl esters of phosphoric acid in which theamine salt constitutes at least 25% by weight, the alkyl groups herereferred to containing from 8 to 18 carbon atoms each. Suitableadditives coming within this group are dodecylamine dodecyl acidphosphate, blends made up of from 25 to 95 of dodecylamine dodecyl acidphosphate and from 75 to 5% of dodecyl dihydrogen phosphate, octylaminedioctyl phosphate, di(decylarnine)dodecyl phosphate, hexadecylaminedodecyl acid phosphate, octadecylamine dioctadecyl phosphate, and blendscontaining 2-ethylhexylamine 2-ethylhexyl acid phosphate andZ-ethylhexyl dihydrogen phosphate in equal proportions. A preferredextreme pressure additive is a blend made up of an alkylamine acid alkylphosphate with an alkyl dihydrogen phosphate, in which blend the aminesalt component is present to the extent of from 25 to 95% by weight.

The anti-wear additive is present in the amount of from 0.5 to 5% and isa compound selected from the group consisting of neutral aryl phosphatesand neutral alkyl aryl phosphates. Representative additives comingwithin this grouping are triphenyl phosphate, tricresyl phosphate, butyldiphenyl phosphate, phenyl dibutyl phosphate, benzyl dicresyl phosphate,trixylyl phosphate and diphenyl cresyl phosphate. A preferred additiveof this class is tricresyl phosphate.

The metal deactivator additive, which is present in the amount of from0.005 to 0.2%, and preferably from 0.01 to 0.1%, by weight, is acompound selected from the group consisting of quinizarin, alizarin,purpurxanthrene, anthrarufin, and chrysazin. The preferred additive ofthis class is quinizarin.

As the foam inhibitor there is employed from 0.0001 to 0.02% of adi(lower alkyl)silicone polymer such as dimethyl silicone, diethylsilicone, methyl ethyl silicone and methyl pentyl silicone. Thepreferred additive or this class is dimethyl silicone.

The lubricant composition of the present invention is illustrated by thefollowing examples.

Example I In this operation a lubricant composition was employed havingthe following composition:

96.78% methyl-Z-ethylhexyl diether of poly(mixed ethylene-propylene)glycol 0.12% dodecylamine dodecyl acid phosphate 0.08% dodecyldihydrogen phosphate 2.0% tricresyl phosphate 1.0%phenyl-a-naphthylamine 0.02% quinizarin 0.001% dimethyl silicone Theglycol diether base fluid employed in the foregoing composition was onewhich had been formed by polymerizing equimolar proportions of ethyleneoxide and 1,2-propylene oxide in the presence of 2-ethylhexanol andthereafter replacing the terminal hydroxy group of the resultingmonoether with a methoxy radical, the diether employed representing amixture having an average molecular weight of approximately 440 andcontaining an average of approximately 2.9 monomer units each ofoxyethylene and 1,2-oxypropylene in the diether molecule. While thisbase fluid had viscosities of 5900, 9.09 and 2.80 cs. at temperatures of65, 100 and 210 F., respectively, the overall compounded lubricant hadthe following viscosity and other indicated physical properties:

Viscosity at 65 F., cs 8390. Viscosity at 100 F., cs 9.95. Viscosity at210 F., cs 2.86.

Viscosity index 155.

Pour point, F Below 75.

Flash point, F 370.

Corrosion properties Noncorrosive to steel,

. magnesium, a l u m inum, copper and silver.

Falex E. P. test, lbs 4500.

Coking test, mgs 70:5.

In the above tabulation of data, the coking test referred to is onewherein the oil in a bath maintained at a con stant level is splashedagainst an overhead inclined plate maintained at a temperature of 600 F.by steel wires on a wheel partially immersed in said oil rotated at aspeed of 1050 R. P. M. The coking value is obtained by measuring theWeight of deposit formed on the underside of the plate in mgs. during a10-hour test period. The load-carrying capacity of the lubricant isdetermined by a Falex E. P. test wherein the conventional equipment isoperated at 300 R. P. M. at a temperature of 70 F., the load at failurebeing recorded in pounds.

This application is a continuation-in-part of application Serial No.383,404, filed September 30, 1953, now abandoned.

We claim:

1. A lubricant composition comprising (a) from to 98% by weight of amixture of methyl-Z-ethylhexyl diethers of poly(oxyethylene 1,2oxypropylene) glycols having approximately equimolar proportions of saidoxyethylene and 1,2-oxypropylene groups, and having a molecular weightbetween about 350 and 700, a viscosity be tween 5,000 and 12,000 cs. at-65 F. and 2.5 and 3.5 cs. at 210 F., a pour point below 65 F., and aflash point above 350 F., (b) from 0.5 to 3% of phenyl-a-naphthylamine,(c) from 0.1 to 0.5% by weight of :a blend of an alkylamine acid alkylphosphate with an alkyl dihydrogen phosphate wherein the amine saltcomponent is present to the extent of from 25 to by weight, the alkylgroups in said ester containing from 8 to 18 carbon atoms each, (d) from0.5 to 5% by weight of tricresyl phosphate, (e) from 0.01 to 0.1% byweight of quinizarin, and (I) from 0.0001 to 0.02% by weight of dimethylsilicone polymer foam inhibitor.

2. A lubricant composition comprising (a) from 90 to 98% by weight of amixture of methyl-Z-ethylhexyl diethers of poly(oxyethylene 1,2oxypropylene) glycols having approximately equimolar proportions of saidoxyethylene and 1,2-oxypropylene groups, and having a molecular weightof approximately 440, a viscosity of about 5900 at 65 F. and 2.8 at 210F., a pour point below -65 F., and flash point above 350 F., (b) from0.5 to 3% of phenyl-a-naphthylamine, (c) from 0.1 to 0.5% by weight of ablend of an alkylamine acid alkyl phosphate with an alkyl dihydrogenphosphate wherein the amine salt component is present to the extent offrom 25 to 95 by weight, the alkyl groups in said ester containing from8 to 18 carbon atoms each, (d) from 0.5 to 5% by weight of tricresylphosphate, (e) from 0.01 to 0.1% by weight of quinizarin, and (f) from0.0001 to 0.02% by weight of dimethyl silicone polymer foam inhibitor.

3. A lubricant composition comprising (a) 96.78% by weight of a mixtureof methyl-2-ethy1hexyl diethers of poly(oxyethylene-1,2-oxypropylene)glycols having approximately equimolar proportions of said. oxyethyleneand 1,2-oxypropylene groups, and having a molecular weight ofapproximately 440, a viscosity of about 5900 at 65 F. and 2.8 at 210 F.,a pour point below 65 F., and a flash point above 350 F., (b) 1.0% ofphenyl-unaphthylamine, (c) 0.2% by weight of a blend of an alkylamineacid alkyl phosphate with an alkyl dihydrogen phosphate wherein theamine salt component is present to the extent of from 25 to 95 byweight, the alkyl groups in said ester containing from 8 to 18 carbonatoms each, (d) 2.0% by weight of tricresyl phosphate, (e) 0.02%

by weight of quinizarin, and (f) 0.001% by weight of di- 2,375,007Larsen May 1, 1945 methyl silicone polymer foam inhibitor. 2,420,953Hunt May 20, 1947 2,425,755 Roberts Aug. 19, 1947 References Cited inthe file of this patent 2,672,447 Stewart Mar. 16, 1954 UNITED STATESPATENTS 5 FOREIGN PATENTS 2,285,853 Downing June 9, 1942 601,419 GreatBritain May 5, 1948

1. A LUBRICANT COMPOSITION COMPRISING (A) FROM 90 TO 98% BY WEIGHT OF AMIXTURE OF METHYL-2-ETHTLHEXYL DIETHERS OFPOLY(OXYETHYLENE-1,2-OXYPROPYLENE) GLYCOLS HAVING APPROXIMATELYEQUIMOLAR PROPORTIONS OF SAID OXYETHYLENE AND 1,2-OXYPROPYLENE GROUPS,AND HAVING A MOLECULAR WEIGHT BETWEEN ABOUT 350 AND 700, A VISCOSITYBETWEEN 5,000 AND 12,000 CS. AT -65*F. AND 2.5 AND 3.5 CS. AT 210*F., APOUR POINT BELOW -65*F., AND A FLASH POINT ABOVE 350*F., (B) FROM 0.5 TO3% OF PHENYL-A-NAPHTHYLAMINE, (C) FROM 0.1 TO 0.5% BY WEIGHT OF A BLENDOF AN ALKYAMINE ACID ALKYL PHOSPHATE WITH AN ALKYL DIHYDROGEN PHOSPHATEWHEREIN THE AMINE SALT COMPONENT IS PRESENT TO THE EXTENT OF FROM 25 TO95% BY WEIGHT, THE ALKYL GROUPS IN SAID ESTER CONTAINING FROM 8 TO 18CARBON ATOMS EACH, (D) FROM 0.5 TO 5% AY WEIGHT OF TRICRESYL PHOSPHATE(E) FROM 0.01 TO 0.1% BY WEIGHT OF QUINIZARIN, AND (F) FROM 0.0001 TO0.02% BY WEIGHT OF DIMETHYL SILICONE POLYMER FOAM INHIBITOR.